Asia can be held if you can also take (or start from) Australia and take Ukraine iirc. It works out to 3 territories defending the entire space. That's literall

Asia can be held if you can also take (or start from) Australia and take Ukraine iirc. It works out to 3 territories defending the entire space. That's literally the same as defending the whole of the Americas. Europe+Africa can also make a sustainable combination, but neither works on its own. Every other pair has too many connections and no way to reduce to a chokepoint.